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Capital Disclosure of components of capital (Details) - CAD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of components of capital [Line Items] |  |  |  |  |
Long-term debt |  | $ 3,361 | $ 3,212 |  |
Increase (decrease) in financial liabilities |  | 149 |  |  |
Exchangeable securities |  | 730 | 326 |  |
Increase (decrease) in exchangeable securities |  | 404 |  |  |
Equity |  | 3,436 | 4,062 | $ 4,134 |
Cash and cash equivalents |  | (703) | (411) | (89) | $ (314)
Increase (decrease) in cash and cash equivalents |  | (292) | (322) | 225 |
Current restricted cash and cash equivalents |  | (71) | (32) |  |
Fair value asset of hedging instruments on long-term debt |  | (2) | (7) |  |
Increase (decrease) in hedging instruments, liabilities |  | 5 |  |  |
Total capital |  | 6,811 | 7,172 |  |
Increase (decrease) in capital |  | (361) |  |  |
Common shares |  |  |  |  |
Disclosure of components of capital [Line Items] |  |  |  |  |
Equity |  | 2,896 | 2,978 |  |
Increase (decrease) in equity |  | (82) |  |  |
Preferred shares |  |  |  |  |
Disclosure of components of capital [Line Items] |  |  |  |  |
Equity |  | 942 | 942 |  |
Increase (decrease) in equity |  | 0 |  |  |
Contributed surplus |  |  |  |  |
Disclosure of components of capital [Line Items] |  |  |  |  |
Equity |  | 38 | 42 | 11 |
Increase (decrease) in equity |  | (4) |  |  |
Deficit |  |  |  |  |
Disclosure of components of capital [Line Items] |  |  |  |  |
Equity |  | (1,826) | (1,455) | (1,496) |
Increase (decrease) in equity |  | (371) |  |  |
Accumulated other comprehensive income |  |  |  |  |
Disclosure of components of capital [Line Items] |  |  |  |  |
Equity | [1] | 302 | 454 | 481 |
Increase (decrease) in equity |  | (152) |  |  |
Non-controlling interests |  |  |  |  |
Disclosure of components of capital [Line Items] |  |  |  |  |
Equity |  | 1,084 | 1,101 | $ 1,137 |
Increase (decrease) in equity |  | (17) |  |  |
TransAlta OCP |  |  |  |  |
Disclosure of components of capital [Line Items] |  |  |  |  |
Current restricted cash and cash equivalents |  | (11) | $ (10) |  |
Increase (decrease) in restricted cash and cash equivalents |  | $ (1) |  |  |
[1] | Refer to Note 29 for details on components of, and changes in, accumulated other comprehensive income (loss).

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